1. Field of the Invention
The present invention relates to disc drive devices and, more specifically, a device incorporated in a DVD player, a DVD recorder, a personal computer, or the like, and capable of driving discs in DVD format (DVD-ROM discs, DVD-RAM discs, DVD-R discs, DVD-RW discs, etc.) for reading (reproducing) data on a real-time basis, such as video and audio, recorded on the DVD-format discs.
2. Description of the Background Art
As is well known, DVD-format discs have such a large storage capacity that they are used mainly for recording and reproducing data on a real-time basis. Data, such as video and audio, that should be recorded and reproduced on a real-time basis is hereinafter called Real-time data. Especially, in writable DVD-format discs, such as DVD-RAM, DVD-R, and DVD-RW discs, a real-time recording (RTR) format is used for recording Real-time data. In the RTR format, Real-time data is compressed with MPEG2 at a compression rate enabling single-speed recording, and then is recorded on a disc. Therefore, the Real-time data recorded in the RTR format (hereinafter, “RTR-format data”) is generally reproduced at single speed (normal speed) in a disc drive device.
Unlike magnetic tapes, discs (especially, optical discs where data can be recorded or reproduced without any contact) have a feature of enabling a quick change of data locations to be read. Using this feature, one conventional scheme is to read data at a speed equal to or faster than single speed, and then sequentially store the read data in memory of the device before reproduction. In this scheme, if data fails to be read due to a scratch or stain on the disc or vibrations of the device (if a read error occurs), such data can be read again while other data stored in memory is being reproduced. In recent years, technology has been so advanced as to enable CD-ROM drives to carry out data processing at 32× to 48× speeds and DVD-ROM drives to carry out at 8× to 16× speeds.
In general, disc drive devices capable of high-speed reading at single or more speed are also capable of low-speed reading. For example, disc drive devices capable of reading DVD-ROM discs at 8× speed at maximum are often capable of reading at quadruple speed and also at double speed. Note that which speeds are supported by a particular disc drive device depend on its vender.
An example technique using the above feature of supporting a plurality of speeds is disclosed in Japanese Patent No. 2570004, in which the reading speed is varied between Real-time data and program data in order to improve efficiency of reading and executing data that does not have to be read or executed on a real-time basis.
In general, data recorded on a disc is more likely to be successfully read at a low speed, compared with when read at a high speed. Therefore, if an error has occurred during high-speed data reading, the data is generally tried to be re-read at the high speed for several times. If an error still occurs, the data is then tried to be read at the low speed. If a plurality of speeds are supported, the reading speed is changed stepwise within the supported speeds, such as from 8× speed, quadruple speed, double speed, and then to single speed.
Here, if the reading speed is changed to the low speed due to the occurrence of an error, and kept thereat for data reading, data reading has to be carried out always at the low speed even in a case where any further errors will not possibly occur. Such low-speed reading is a waste of time. Therefore, in general, after being changed to the low speed due to the occurrence of an error, the reading speed is returned to the high speed in such a case as after data reading has been carried out for a predetermined number of sectors; after a predetermined time passes; when data reading is carried out for a sector away from the one where the error has occurred, or others.
However, to re-read data after an error has been detected, it takes several tens to hundreds of milliseconds (seek time). Moreover, a process for decelerating or accelerating the reading speed can take several hundreds to thousands of milliseconds at a time. Therefore, such processing time greatly interferes with reproduction of Real-time data, such as RTR-format data. Especially, as for a disc that is error-prone at high-speed reading, if the reading speed is decelerated or accelerated every time when an error occurs with a sufficient amount of data not yet been stored in memory, video and audio recorded on the disc cannot be played back without interruption because data cannot be read during the deceleration or acceleration process.